One possible way of obtaining 3D coordinates of an 3D object by from 2D digital image is carried out by utilizing, what is commonly known as the Original “Structured Light Technique”, which is usually based on irradiating (i.e., projecting, e.g., white line(s), or strip(s), onto the surface of a 3D object, employing corresponding 2D image processing technique for distinguishing these lines/strips from other portions of the object (i.e., by usually utilizing simple threshold techniques), after which a known triangulation algorithm is utilized for calculating the 3D coordinates of points residing on these lines/strips. There is a well known ambiguity problem associated with the simultaneous projection of several lines onto the surface of the object, i.e., there is no reliable way to distinguish between different white lines of the 2D image in the presence of noise, because some points could be missed and other points could be falsely assigned to the wrong line. One possible approach to overcome these problems is to project only one line at a time, and, then, to process the resulting 2D image white points as corresponding to respective known lines. However, the problem with the aforesaid ‘one white-line technique’ is that only the coordinates of the points positioned on this line will be obtained. Conventional techniques try to solve this problem (i.e., getting a larger set of 3D points), by physically moving the line to various locations, or, alternatively, by using several lines, which are switched on and off. Both solutions are very long, inconvenient and time consuming processes and they require complicated hardware or mechanical tools.
Fitracks discloses in a co pending IL Patent application serial No. 154345 a method and apparatus for determining the 3-dimensional shape and dimensions of an object. However, Fitracks teaches utilizing a number of parallel light sources that are switched “ON” and “OFF” according to an acquisition algorithm. However, according to Fitracks, the number of the lines is limited to eight and, in any case, can not be significantly increased, thus restricting 3D resolution of Fitrack's scanner. In addition, Fitracks utilizes laser light, which is unacceptable in applications where the tested object is a human face.
In order to solve problems caused by use of white strips/lines, a pattern that includes lines of different colors is used. Then, different lines are projected at the same time, and corresponding software distinguishes between the lines by their respective colors on the 2D image. However, the problem with the latter approach is that it can only be applied for white or homogeneously colored (say grey, yellow or green) colored objects, because when projected on a colored object, such as a human face, one or more of the colored lines could be similar to the colors in the object, which would render the color recognition technique unreliable.
U.S. Pat. No. 6,028,672 discloses high speed 3D imaging method, which is implemented, according to one embodiment, by two cameras, for creating stereo-pairs, and according to another embodiment, by one camera. However, using one camera as disclosed by U.S. Pat. No. 6,028,672, requires utilization of several mirrors and a LCD shutter, which makes the disclosed system expensive. In addition, the system of U.S. Pat. No. 6,028,672 requires very accurate spectral device, the price of which is normally in the range 730-1,395 US$, which is relatively high. Furthermore, the high accuracy spectral device is critical for obtaining the required results. However, a problem with this method is that, the spectrum of the light reflected from the object under test, is dictated according to the absorption spectrum of the reflecting surface, and, even worse, according to the reflection angle and texture of the reflecting surface.
U.S. Pat. No. 6,413,084 discloses a method and system for scanning an object, in which each one of the lines is assigned a bar-code like marker above it. However, this system can not be applied to human face, because most of the markers will not be reliably visible by the camera, or reliably resolved.
U.S. Pat. No. 6,438,272 discloses a method and apparatus for three dimensional surface contouring using a digital video projection system. According to U.S. Pat. No. 6,438,272, one camera is utilized, as well as color strips with separators. However, the aforesaid method/apparatus utilize a phase detection algorithm, which is incapable of handling missing sections in the lines. Therefore, a crucial factor, in operating the system of U.S. Pat. No. 6,438,272, is that the calibration pattern as a whole must be seen by the camera with no ‘holes’/missing sections. In addition, the method disclosed in U.S. Pat. No. 6,438,272 could be employed, as indicated therein, only on white or homogeneously colored surfaces, the angle of acquisition (i.e., of the face) must be very carefully chosen (to ensure contiguity of the pattern), and the optical elements of the camera must be of high precision. Therefore, this apparatus could be potentially exploited mostly by laboratories.
Other solutions are aimed at solving some of the above-described drawbacks. However, these solutions employ rather complex mathematical algorithms which are mostly highly unreliable in the real life environment, and/or use laser and/or digital projectors, which is a drawback by itself because of the cost.
All of the above-mentioned solutions have not provided a satisfactory solution to the problem of obtaining a 3D scanning of an object by means of very low cost, compactly designed, and reliable 3D scanning apparatus.
It is therefore an object of the present invention to provide a compact 3D scanning apparatus, which is inexpensive, easy to operate and reliable.
It is another object of the present invention to provide a 3D scanning apparatus that is capable of reliably handling non-uniformly colored shape of an object.
It is still another object of the present invention to provide a 3D scanning apparatus wherein the accuracy of the arrangement of its optical components, relative to one another, and the quality of the optical components are not critical to its proper functioning.
It is a further object of the present invention to provide a method for reliably obtaining a 3D model of a 3D object.
It is a further object of the present invention to provide a 3D scanning apparatus capable of operating rapidly or essentially in ‘real-time’.
Other objects and advantages of the invention will become apparent as the description proceeds.